Thursday, May 8, 2014

A young male with unknown past medical history presents with AMS and tachycardia. EMS was called by a roommate after the patient was noticed to be nonverbal and lethargic. He reportedly took meth and had a recent drinking binge, but has not had alcohol for the last 2 days. His HR was 160 on arrival of EMS, and they gave him adenosine 6 mg and 12 mg and 500 cc NS, but with no response. The preshospital ECG and strips are not available. The patient was restless, agitated, and nonverbal on arrival to ED, with elevated HR at 150. Here is the first ED ECG:

What is the likely diagnosis?

There is sinus tachycardia, a prolonged QRS (computer read it as 114 ms, previous ECG with 102 ms). There is a large R-wave in lead aVR. These findings are nearly pathognomonic of, or at least highly suspicious for, tricyclic antidepressant (TCA) overdose.

One can read about management of TCA overdose in many places, and I have put some links to lifeinthefastlane below.

A few important points:

1. An R-wave in lead aVR greater than 3 mm, or an R/S ratio greater
than 0.7, is highly suspicious for sodium channel blockade, which is the
most important of the many toxicities of TCA overdose.

2.In 49 patients with known TCA overdose,
a maximum limb lead QRS duration greater than 100 ms was 100% sensitive for
detecting patients who will seize, and seizure is a harbinger of
cardiovascular collapse. At this cutoff of 100 ms, however, the
specificity was not perfect. Of 11 patients with an initial QRS
duration of 100-119 ms, 2 (18%) had seizures, and of 22 with an initial
QRS duration of 100-139 ms, 4 (18%) had seizures. Of 14 with initial
QRS of 140 ms or longer, 8 (56%) had seizures. No patient with a QRS of
less than 160 ms had ventricular dysrhythmias.

2a. In an unselected
population with suspicion of overdose, a minimally wide QRS (less than
110 ms) will be much less specific; furthermore, it is likely that
frequent serial ECGs, by detecting an increasing QRS duration, will
detect those at risk of toxicity. On the other hand, administration of
bicarbonate, the antidote, is relatively safe compared with a seizure.
If the diagnosis is unclear, narrowing of a widened QRS on ECG following
sodium bicarbonate administration (1-2meq/kg) adds further support that
pharmacologic sodium blockade is present.

When it became clear that the patient had sinus tach and not PSVT, his presentation was recognized as an overdose or drug toxicitiy. But because the physicians were so focused on his tachycardia, meth use, and rhythm, they did not look for or appreciate the findings of TCA overdose. We in emergency medicine obtain ECGs in overdoses mostly to look for TCA findings. So when you get an ECG in this situation, look for them!

Much later, the roommate called and reported that 20 amitryptiline (unknown mg per dose) were missing. Fortunately, the patient had not had any adverse outcome by that time.
He was given multiple amps of bicarb and a bicarbonate drip. He remained delirious and was given 3 mg of physostigmine (after pretreatment with 2 mg of lorazepam to prophylax against seizures). His delirium greatly improved and he was then able to follow commands.

He had a prolonged stay in the ICU requiring days of bicarbonate. The tox screen only showed amitryptiline.

VERY nice case Steve! Just curious - Was there no response at all to the Adenosine? (not even transient slowing of the rate to confirm sinus tachycardia?). THANKS again for presenting this illustrative case - :)

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Disclaimer

Cases come from all over the world. Patient identifiers have been redacted or patient consent has been obtained. The contents of this site have not been reviewed nor approved by Hennepin County Medical Center and any views or opinions expressed herein do not necessarily reflect the views or opinions of Hennepin County Medical Center.